The process of depositing layers of material on a semiconductor wafer, or other substrate, usually involves heating the substrate and holding it a short distance from the source of a stream of deposition (or processing) gases. In a plasma enhanced CVD (PECVD) process, the gas is also excited to a plasma state. To deposit material on a substrate, the substrate support, also called the substrate support pedestal, is heated. The substrate support is typically made of aluminum having an anodized surface. Heating is typically needed to provide reaction energy for deposition reactions to occur.
During CVD processing, ideally the injected process gases would deposit only on the substrate surface. However, in reality some gas molecules deposit on the process chamber surfaces other than the surface of the substrate. All chamber surfaces inside the processing surface chamber are susceptible to being coated by the constituents of the deposition gases.
When the buildup of surface deposits on the inside of the processing chamber becomes thick, flakes or other particles of the deposited material can fall from the surface of the chamber onto the substrate being processed, potentially causing a defect. To avoid this problem, the inside surfaces of the processing chamber are periodically cleaned by, for example, etching (plasma cleaning) their surfaces with fluorine-containing species and oxidizer mixtures, such as CF.sub.4, NF.sub.3 or C.sub.2 F.sub.6 and O.sub.2 mixtures. Other cleaning compositions can also be used. While doing so removes the deposits, the fluorine species also attack the substrate support surface of the base of the substrate support. These cleaning sessions cause erosion, wear and nodule growth on the typically anodized aluminum surface of the substrate support. Furthermore, variations in the quality of the anodization or other corrosion resistant coating on the support surface of the substrate support can result in undesirable differences in electrical and chemical (insulating) properties across the support surface; these differences can cause undesirable variations in the plasma which can contribute to non-uniform deposition on the wafer or the substrate's surface.
Bare aluminum surfaces can also be used for the support surface of the substrate support. However, such bare aluminum surfaces are subject to attack by the fluorine-containing species and oxidizer mixture during the chemical cleaning; this results in an aluminum fluoride (AlF) film growth causing process parameters to drift. The aluminum fluoride film is also subject to cracking and peeling causing particle contamination within the vacuum processing chamber.